I'm a longtime runner having run over 80 marathons and ultramarathon but in the last year or so my runs have gotten terrible. After 3 or 4 miles my throat and chest get increasingly tight and it seems hard to get a good deep breath. So, I went in for a physical: Everything looks fine. Went to a cardiologist and had an ultrasound and several other tests: Everything looked good. Went to a pulmenary doc and had a battery of tests: all fine. Lastly went to an ENT: Everything looked good. Extremely frustrated with a lot of money spent and zero answers. And the problem has about shut down my running. Any suggestions??